New fiber is tougher than Kevlar

Researchers at Northwestern University have nanoengineered a new kind of fiber that they say is tougher than Kevlar.

With Department of Defense funding, the team has created a high performance fiber from carbon nanotubes that they say is remarkably tough, strong, and resistant to failure.

"A big issue in engineering fibers is that they are either strong or ductile — we want a fiber that is both," says says professor Horacio Espinosa.

"The fibers we fabricated show very high ductility and a very high toughness. They can absorb and dissipate large amounts of energy before failure. We also observed that the strength of the material stays very, very high, which has not been shown before. These fibers can be used for a wide variety of defense and aerospace applications."

These include bulletproof vests, parachutes, or composite materials for use in vehicles, airplanes and satellites.

While carbon nanotubes individually have one of the highest strengths of any material in nature, they lose their strength when they're bundled together, as the tubes start to laterally slip between one other.

But the Northwestern team added a polymer to the nanotubes to bind them together, and then spun the resulting material into yarns. Then they tested the strength and failure rates of the material using SEM testing, which uses a powerful microscope to observe the deformation of materials under a scanning electron beam.

"We learned on multiple scales how this material functions," said Tobin Filleter, a postdoctoral researcher in Espinosa’s team. "We’re going to need to understand how molecules function at these nanometer scales to engineer stronger and tougher fibers in the future."

The result is a material that is tougher than Kevlar — in other words, it has a higher ability to absorb energy without breaking. But Kevlar still has a higher resistance to failure. Next, the team hopes to better engineer the interactions between carbon nanotube bundles and between the nanotubes within the bundle itself.

"Carbon nanotubes, the nanoscale building blocks of the developed yarns, are still 50 times stronger than the material we created," says Mohammad Naraghi, a postdoctoral researcher in Espinosa’s group.

"If we can better engineer the interactions between bundles, we can ake the material stronger."

The group is currently looking at techniques — like covalently crosslinking tubes within bundles using high-energy electron radiation – to help improve those interactions.